This invention relates generally to the art of slide projectors and more specifically concerns a slide projector having multiple image projection systems.
The slide projector which is the subject of this application is an improvement to the projector disclosed and claimed in U.S. Pat. No. 4,165,161, issued on Aug. 21, 1979 to Gideon A. Kramer, titled: Multiple Optics Slide Projector. The subject matter of U.S. Pat. No. 4,165,161 is a two-image, lap-dissolve slide projector using a single circular slide tray. Although the projector disclosed therein was suitable for its intended purpose, improvements to its efficiency and operation were possible. The major areas of improvement in the present invention include (1) the slide handling system, (2) the drive and control system for the slide tray, and (3) the image alignment system.
Proper slide handling is important, because of the possibility of slide jams due to the sequence of slide movement in the projector, inherent in its design, which provides the dual image capability. Furthermore, an accurate, positive drive for the slide tray, as well as continuous, accurate knowledge of the position of the slide tray, relative to a reference point, is important to the proper operation of such a projector, especially because many of the individual elements are capable of independent actuation. Otherwise, it would not be possible to have a projector with a random access to the slide tray and other sophisticated capabilities.
In addition, proper image alignment is important. In conventional slide projectors, even existing dual image slide projectors, lateral movement of the images on the screen results in what is referred to as image keystoning, i.e. as the image is moved laterally, it tends to become shorter at one end relative to the other. The effect increases as the distance the image moves is increased, and can be quite noticeable. The keystoning effect thus has heretofore discouraged the use of more sophisticated image techniques, such as overlapping or separated simultaneous imaging, in audio-visual presentations using multiple images.
Accordingly, it is a general object of the present invention to provide a dual image, single tray slide projector which overcomes one or more of the disadvantages of the prior art discussed above.
It is an additional object of the present invention to provide such a slide projector which includes structural features designed to maintain positive control over the movement of slides in the projector and to minimize the possibility of a slide jam during operation of the projector.
It is another object of the present invention to provide such a projector which includes structural features designed to provide accurate and continuous knowledge of the position of the slide tray.
It is a further object of the present invention to provide such a projector which includes structural features designed to provide substantially undistorted images over a relatively wide lateral range of movement of the images.
It is yet another object of the present invention to provide such a projector which is capable of recognizing machine malfunction and/or incorrect human intervention and to stop operation of the projector, if necessary.
It is an additional object of the present invention to provide such a projector which has many elements capable of independent actuation and control.